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Hotspots
(in yellow) with rising from the (in red). Lower diagram illustrates a hotspot track caused by their relative movement.}} In , the places known as hotspots or hot spots are regions thought to be fed by underlying that is anomalously hot compared with the surrounding mantle. A hotspot track results if such a region is moving relative to the mantle. A hotspot's position on the Earth's surface is independent of . There are two hypotheses that attempt to explain their origins. One suggests that hotspots are due to s that rise as thermal s from the core–mantle boundary. The other hypothesis is that lithospheric extension permits the passive rising of melt from shallow depths. This hypothesis considers the term "hotspot" to be a misnomer, asserting that the mantle source beneath them is, in fact, not anomalously hot at all. Well-known examples include the , and s. Origin The origins of the concept of hotspots lie in the work of , who postulated in 1963 that the formation of the resulted from the slow movement of a across a hot region beneath the surface. It was later postulated that hotspots are fed by narrow streams of rising from the Earth's in a structure called a . Whether or not such mantle plumes exist is the subject of a major controversy in Earth science. Estimates for the number of hotspots postulated to be fed by mantle plumes have ranged from about 20 to several thousands, over the years, with most geologists considering a few tens to exist. , , , , and are some of the most active volcanic regions to which the hypothesis is applied. Composition Most hotspot volcanoes are (e.g., , ). As a result, they are less explosive than volcanoes, in which water is trapped under the overriding plate. Where hotspots occur in , ic rises through the continental crust, which melts to form s. These s can form violent eruptions. For example, the was formed by some of the most powerful volcanic explosions in geologic history. However, when the rhyolite is completely erupted, it may be followed by eruptions of basaltic magma rising through the same lithospheric fissures (cracks in the lithosphere). An example of this activity is the in British Columbia, which was created by an early complex series of and eruptions, and late extrusion of a sequence of basaltic lava flows. The hotspot hypothesis is now closely linked to the hypothesis. Comparison with island arc volcanoes Hotspot volcanoes are considered to have a fundamentally different origin from volcanoes. The latter form over zones, at converging plate boundaries. When one oceanic plate meets another, the denser plate is forced downward into a deep ocean trench. This plate, as it is subducted, releases water into the base of the over-riding plate, and this water mixes with the rock, thus changing its composition causing some rock to melt and rise. It is this that fuels a chain of volcanoes, such as the , near . Hotspot volcanic chains has moved over the , creating that stretch across the Pacific}} is the most active shield volcano in the world. The volcano erupted nonstop from 1983 to 2018 and it is part of the .}} is a large shield volcano. Its and it is part of the .}} is a dormant submarine volcano and it is part of the .}} is the youngest seamount of the . Its last eruption was on 6 April 2011.}} is the tallest volcano in the . It is dormant and it has growing on the volcano.}} is a massive shield volcano in the . Its last eruption was in 1801.}} The joint /hotspot hypothesis envisages the feeder structures to be fixed relative to one another, with the continents and drifting overhead. The hypothesis thus predicts that time-progressive chains of volcanoes are developed on the surface. Examples are , which lies at the end of a chain of extinct calderas, which become progressively older to the west. Another example is the Hawaiian archipelago, where islands become progressively older and more deeply eroded to the northwest. Geologists have tried to use hotspot volcanic chains to track the movement of the Earth's tectonic plates. This effort has been vexed by the lack of very long chains, by the fact that many are not time-progressive (e.g. the ) and by the fact that hotspots do not appear to be fixed relative to one another (e.g. and .) Postulated hotspot volcano chains * ( ) * ( ) * (Gough and ) * ( ) * ( ) * ( ) * ( ) * ( ) * ( ) * – ( ) * – ( ) * ( ) * – Island chain ( ) * – – chain ( ) * ( ) * ( ) List of volcanic regions postulated to be hotspots Eurasian Plate * (8) ** , w= 1 az= 082° ±8° rate= 12 ±2 mm/yr * (14) ** *** Eurasian Plate, w= .8 az= 075° ±10° rate= 5 ±3 mm/yr *** North American Plate, w= .8 az= 287° ±10° rate= 15 ±5 mm/yr ** Possibly related to the North Atlantic continental rifting (62 Ma), . * (1) ** *** Eurasian Plate, w= .5 az= 110° ±12° *** North American Plate, w= .3 az= 280° ±15° * (15) ** * hotspot (46) ** , az= 000° ±15° African Plate * (47) ** * hotspot (13) ** , w= .3 az= 046° ±12° * hotspot (40) ** , w= .2 az= 030° ±15° * (6) ** , w= .5 az= 045° ±8° * (29, misplaced in map) ** , w= .2 az= 030° ±15° rate= 16 ±8 mm/yr ** Possibly related to the , 30 Ma. * hotspot (17) ** , w= .3 az= 032° ±3° rate= 15 ±5 mm/yr * hotspot (48) ** , w= .3 az= 055° ±15° rate= 8 ±3 mm/yr * (18) ** , w= 1 az= 094° ±8° rate= 20 ±4 mm/yr * (28) ** , w= .8 az= 040° ±10° * hotspot (19) ** , w= .2 az= 060° ±30° * (34) ** , w= 1 az= 078° ±5° rate= 20 ±3 mm/yr * hotspot (49), at 40°19' S 9°56' W. ** , w= .8 az= 079° ±5° rate= 18 ±3 mm/yr * (42), at 37°07′ S 12°17′ W. ** * (Vema Seamount, 43), at 31°38' S 8°20' E. ** ** Related maybe to the (c. 132 Ma) through the . * Discovery hotspot (50) ( ) ** , w= 1 az= 068° ±3° * hotspot (51) ** * (27) ** , w= .3 az= 074° ±6° * (33) ** , w= .8 az= 047° ±10° rate= 40 ±10 mm/yr ** Possibly related to the (main events: 68.5–66 Ma) * hotspot (21) ** , w= .5 az=118 ±10° rate=35 ±10 mm/yr Antarctic Plate * hotspot (25) ** , w= .5 az= 080° ±12° * hotspot (52) ** , w= .8 az= 109° ±10° rate= 25 ±13 mm/yr ** Possibly related to the geologic province (183 Ma) * (20) ** , w= .2 az= 050° ±30° rate= 3 ±1 mm/yr ** and could be part of the Kerguelen hotspot trail (St. Paul is probably not another hotspot) ** Related maybe to the (130 Ma) * hotspot (53) ** , w= .2 az= 030° ±20° * (2) ** , w= .2 az= 325° ±7° * (54) ** South American Plate * (41) ** , w= 1 az= 264° ±5° * (9) ** , w= 1 az= 266° ±7° ** Possibly related to the (c. 200 Ma) * hotspot (55) ** North American Plate * (56) ** , w= .3 az= 260° ±15° * (44) ** , w= .8 az= 235° ±5° rate= 26 ±5 mm/yr ** Possibly related to the (17–14 Ma). * (32) ** , w= 1 az= 240°±4° rate= 30 ±20 mm/yr * (45) ** ( ) Indo-Australian Plate * hotspot (22) ** , w= .8 az= 351° ±10° * (39) ** , w= .8 az= 007° ±5° rate= 63 ±5 mm/yr * (30) ** , w= .3 az= 000° ±15° rate= 65 ±3 mm/yr Nazca Plate * (16) ** , w= 1 az= 084° ±3° rate= 80 ±20 mm/yr * hotspot (36) ** , w= .3 az= 083° ±8° * (7) ** , w= 1 az= 087° ±3° rate= 95 ±5 mm/yr * (10) ** *** Nazca Plate, w= 1 az= 096° ±5° rate= 55 ±8 mm/yr *** Cocos Plate, w= .5 az= 045° ±6° ** Possibly related to the (main events: 95–88 Ma). Pacific Plate , creating the in the }} * (23) ** , w= 1 az= 316° ±5° rate= 67 ±5 mm/yr ** Possibly related to the (125–120 Ma). * / (57) ** , w= 1 az= 292° ±3° rate= 80 ±6 mm/yr * (24) ** , w= 1 az= 289° ±6° rate= 105 ±10 mm/yr * North Austral/President Thiers ( , 58) ** , w= (1.0) azim= 293° ± 3° rate= 75 ±15 mm/yr * (Arago Seamount, 59) ** , w= 1 azim= 296° ±4° rate= 120 ±20 mm/yr * hotspot ( , 60) ** , w= 0.8 az= 300° ±4° * (35) ** , w= .8 az= 285°±5° rate= 95 ±20 mm/yr * Crough hotspot ( , 61) ** , w= .8 az= 284° ± 2° * (31) ** , w= 1 az= 293° ±3° rate= 90 ±15 mm/yr * (38) ** , w= .8 az= 295°±5° rate= 109 ±10 mm/yr * (26) ** , w= .5 az= 319° ±8° rate= 93 ±7 mm/yr * hotspot (4) ** , w= 1 az= 289° ±4° rate= 135 ±20 mm/yr * (12) ** , w= 1 az= 304° ±3° rate= 92 ±3 mm/yr * hotspot (37) ** * hotspot (11) ** , w= .8 az= 292° ±5° rate= 80 ±10 mm/yr * (5) ** , w= 1 az= 321° ±5° rate= 43 ±3 mm/yr * (3) ** , w=.8 az= 306° ±4° rate= 40 ±20 mm/yr Former hotspots * Euterpe/Musicians hotspot ( ) * * References